Sep 4, 2025 · Sep 5, 2025
diff --git a/lib/matplotlib/backends/backend_qt.py b/lib/matplotlib/backends/backend_qt.py
 from collections import namedtuple
 import functools
 import os
 import sys
        self._timer.stop()


 Crosshair = namedtuple('Crosshair', 'x, y, x0, x1, y0, y1')


 class FigureCanvasQT(FigureCanvasBase, QtWidgets.QWidget):
    required_interactive_framework = "qt"
    _timer_cls = TimerQT
    def __init__(self, figure=None):
        _create_qApp()
        super().__init__(figure=figure)
        self._crosshair = None

        self._draw_pending = False
        self._is_drawing = False
        y = self.figure.bbox.height / self.device_pixel_ratio - pos.y()
        return x * self.device_pixel_ratio, y * self.device_pixel_ratio

    def _update_crosshair(self, x, y):
        previous_crosshair = self._crosshair
        ax = self.inaxes((x, y))
        if ax is None:
            self._crosshair = None
        else:
            bbox = ax.get_position()  # in figure coords
            x0 = int(bbox.x0 * self.width())
            x1 = int(bbox.x1 * self.width())
            y0 = int((1 - bbox.y0) * self.height())
            y1 = int((1 - bbox.y1) * self.height())
            self._crosshair = Crosshair(x, y, x0, x1, y0, y1)
        needs_repaint = previous_crosshair is not None or self._crosshair is not None
        return needs_repaint

    def enterEvent(self, event):
        # Force querying of the modifiers, as the cached modifier state can
        # have been invalidated while the window was out of focus.
    def mouseMoveEvent(self, event):
        if self.figure is None:
            return
        mouse_xy = self.mouseEventCoords(event)
        needs_repaint = self._update_crosshair(*mouse_xy)
        if needs_repaint:
           self.repaint()
        MouseEvent("motion_notify_event", self,
                   *self.mouseEventCoords(event),
                   *mouse_xy,
                   buttons=self._mpl_buttons(event.buttons()),
                   modifiers=self._mpl_modifiers(),
                   guiEvent=event)._process()
diff --git a/lib/matplotlib/backends/backend_qtagg.py b/lib/matplotlib/backends/backend_qtagg.py
                ctypes.c_long.from_address(id(buf)).value = 1

            self._draw_rect_callback(painter)

            if self._crosshair is not None:
                x = self._crosshair.x
                y = rect.height() - int(self._crosshair.y)
                x0 = rect.left() + self._crosshair.x0
                x1 = rect.left() + self._crosshair.x1
                y0 = rect.top() + self._crosshair.y0
                y1 = rect.top() + self._crosshair.y1
                painter.setPen(QtGui.QPen(QtCore.Qt.GlobalColor.red))
                painter.drawLine(x0, y, x1, y)
                painter.drawLine(x, y0, x, y1)
        finally:
            painter.end()
Original file line number	Diff line number	Diff line change
		@@ -1,3 +1,4 @@
		from collections import namedtuple
		import functools
		import os
		import sys
Expand DownExpand Up		@@ -213,6 +214,9 @@ def _timer_stop(self):
		self._timer.stop()


		Crosshair = namedtuple('Crosshair', 'x, y, x0, x1, y0, y1')


		class FigureCanvasQT(FigureCanvasBase, QtWidgets.QWidget):
		required_interactive_framework = "qt"
		_timer_cls = TimerQT
Expand All		@@ -231,6 +235,7 @@ class FigureCanvasQT(FigureCanvasBase, QtWidgets.QWidget):
		def __init__(self, figure=None):
		_create_qApp()
		super().__init__(figure=figure)
		self._crosshair = None

		self._draw_pending = False
		self._is_drawing = False
Expand DownExpand Up		@@ -305,6 +310,21 @@ def mouseEventCoords(self, pos=None):
		y = self.figure.bbox.height / self.device_pixel_ratio - pos.y()
		return x * self.device_pixel_ratio, y * self.device_pixel_ratio

		def _update_crosshair(self, x, y):
		previous_crosshair = self._crosshair
		ax = self.inaxes((x, y))
		if ax is None:
		self._crosshair = None
		else:
		bbox = ax.get_position() # in figure coords
		x0 = int(bbox.x0 * self.width())
		x1 = int(bbox.x1 * self.width())
		y0 = int((1 - bbox.y0) * self.height())
		y1 = int((1 - bbox.y1) * self.height())
		self._crosshair = Crosshair(x, y, x0, x1, y0, y1)
		needs_repaint = previous_crosshair is not None or self._crosshair is not None
		return needs_repaint

		def enterEvent(self, event):
		# Force querying of the modifiers, as the cached modifier state can
		# have been invalidated while the window was out of focus.
Expand DownExpand Up		@@ -344,8 +364,12 @@ def mouseDoubleClickEvent(self, event):
		def mouseMoveEvent(self, event):
		if self.figure is None:
		return
		mouse_xy = self.mouseEventCoords(event)
		needs_repaint = self._update_crosshair(*mouse_xy)
		if needs_repaint:
		self.repaint()
		MouseEvent("motion_notify_event", self,
		*self.mouseEventCoords(event),
		*mouse_xy,
		buttons=self._mpl_buttons(event.buttons()),
		modifiers=self._mpl_modifiers(),
		guiEvent=event)._process()
Expand Down
Original file line number	Diff line number	Diff line change
Expand Up		@@ -68,6 +68,17 @@ def paintEvent(self, event):
		ctypes.c_long.from_address(id(buf)).value = 1

		self._draw_rect_callback(painter)

		if self._crosshair is not None:
		x = self._crosshair.x
		y = rect.height() - int(self._crosshair.y)
		x0 = rect.left() + self._crosshair.x0
		x1 = rect.left() + self._crosshair.x1
		y0 = rect.top() + self._crosshair.y0
		y1 = rect.top() + self._crosshair.y1
		painter.setPen(QtGui.QPen(QtCore.Qt.GlobalColor.red))
		painter.drawLine(x0, y, x1, y)
		painter.drawLine(x, y0, x, y1)
		finally:
		painter.end()

Expand Down